The distance b from point A to line N must be the point with the smallest distance from point A to all points on line B (this need not be explained, simply because it is infinite, so ... Hehe, you can explain it in detail if you don't understand)

Conclusion: Come up with the conclusion that c≤b out of thin air.

The distance a between a and b is actually one of all distances from a to a point on n, because the distance b from a to a straight line n is the smallest in the above case.

So b≤a

To sum up, choose option D (this question is very simple, that is, don't think about chaos, first sort the distances of various concepts in your mind, and then add symbols)

22 questions

The first question is simple. Take k= 1. At this time, (Sk)=(a 1) is substituted into (a 1) to get (a2)=2.

Then according to (ak)=(Sk)-(Sk- 1)

Simplify (ak) to get (ak+ 1)-(ak- 1)=2.

(a 1)= 1 (ak=2) It is not difficult to see that the difference between the two terms is 2 (AK) = K.

That is, (an)=n

the second question

Typing is really unpleasant.

I'll show you a website/a/a/20070608/000235 _ 5.htm _ 5.htm.

Order on demand

The second question of this question is this type, such as generally telling you.

(ak+ 1)= constant *(ak)

This time, we changed Changshu to a value that varies with k, so we can't directly use the knowledge of geometric series, but should combine other knowledge.

As long as you are patient and take every change of k into account, the final result can be simplified to a simpler form.